1. Field of the Invention
The present invention relates to a holographic information recording and/or reproducing apparatus, and more particularly, to a single-side-incidence holographic information recording and/or reproducing apparatus in which a signal beam and a reference beam are incident on the same surface of a holographic data storage medium.
2. Description of the Related Art
Recording information in a holographic data storage comprises storing information in the form of an interference pattern in a material, such as, a photopolymer, which reacts according to intensity of light. The interference pattern is formed by using two laser beams. That is, the interference pattern is formed by a reference beam and a signal beam interfering with each other and incident on a photosensitive storage medium. The interference pattern causes chemical or physical changes in the photosensitive storage medium, and thus information can be recorded. In order to reproduce information from the recorded interference pattern, a reference beam similar to the beam used when the information was recorded is emitted (or irradiated) to the interference pattern recorded in the photosensitive storage medium. The emitted reference beam is diffracted by the interference pattern, thereby restoring (or reproducing) a signal beam, and thus reproducing the information.
Recording methods using this hologram technology include a volume holographic method in which information is recorded and/or reproduced in units of pages, and a microholographic method in which information is recorded and/or reproduced in units of single bits. Although the volume holographic method has an advantage in that a large amount of information can be processed at the same time, it is difficult for the method to be commercialized and adapted to an information storage apparatus for general consumer use because an optical system should be very precisely adjusted.
Meanwhile, in the microholographic method, two condensed light beams are made to interfere with each other at the focal points of the beams, thereby forming a fine interference pattern. Then, by moving this interference pattern across the plane of a storage medium, a plurality of patterns are recorded to form a recording layer. By superimposing the recording layers in the depth direction of the storage medium, patterns are recorded, thereby recording information in a 3-dimensional (3D) manner.
However, a typical microholographic recording and/or reproducing apparatus is provided with multiple optical systems for generating a signal beam and a reference beam, i.e., an optical system for a signal beam and an optical system for a reference beam on each side (or opposite sides) of a storage medium, respectively. The multiple optical systems are cost prohibitive and are complicated to arrange for precision, and increase the size of the apparatus.
Also, in the field of optical recording devices, to increase capacity, necessity for increasing the storage capacity and transmission rate of information storage media and necessity for recording and/or reproducing multiple channels also increase. In order to satisfy these needs, implementation of a fast access time for the system and the storage medium is necessary.